Method and system for frame formats for MIMO channel measurement exchange

ABSTRACT

A method and system for frame formats for MIMO channel measurement exchange is provided. Aspects of a method for communicating information in a communication system may comprise transmitting data via a plurality of radio frequency (RF) channels utilizing a plurality of transmitting antenna, receiving feedback information via at least one of a plurality of RF channels, and modifying a transmission mode based on the feedback information. Aspects of a method for communicating information in a communication system may also comprise receiving data via a plurality of receiving antenna, transmitting feedback information via at least one of the plurality of RF channels, and requesting modification of a transmission mode for the received data in transmitted response messages comprising the feedback information.

CROSS-REFERENCE TO RELATED APPLICATIONS/INCORPORATION BY REFERENCE

This application makes reference to, claims priority to, and claims thebenefit of U.S. Provisional Application Ser. No. 60/636255 filed Dec.14, 2004.

This application also makes reference to U.S. patent application Ser.No. ______ (Attorney Docket No. 16307US02) filed ______.

All of the above stated applications are hereby incorporated herein intheir entirety.

FIELD OF THE INVENTION

Certain embodiments of the invention relate to wireless networking. Morespecifically, certain embodiments of the invention relate to a methodand system for frame formats for MIMO channel measurement exchange.

BACKGROUND OF THE INVENTION

The Institute for Electrical and Electronics Engineers (IEEE), inresolution IEEE 802.11, also referred as “802.11”, has defined aplurality of specifications which are related to wireless networking.Among them are specifications for “closed loop” feedback mechanisms bywhich a receiving mobile terminal may feed back information to atransmitting mobile terminal to assist the transmitting mobile terminalin adapting signals which are sent to the receiving mobile terminal.

Smart antenna systems combine multiple antenna elements with a signalprocessing capability to optimize the pattern of transmitted signalradiation and/or reception in response to the communications mediumenvironment. The process of optimizing the pattern of radiation issometimes referred to as “beamforming,” which may utilize linear arraymathematical operations to increase the average signal to noise ratio(SNR) by focusing energy in desired directions. In conventional smartantenna systems, only the transmitter or the receiver may be equippedwith more than one antenna, and may typically be located in the basetransceiver station (BTS) where the cost and space associated with smartantenna systems have been perceived as more easily affordable than onmobile terminals such as cellular telephones. Such systems are alsoknown as multiple input single output (MISO) when a multiple antennatransmitter is transmitting signals to a single antenna receiver, orsingle input multiple output (SIMO) when a multiple antenna receiver isreceiving signals that have been transmitted from a single antennatransmitter. With advances in digital signal processing (DSP) integratedcircuits (ICs) in recent years, multiple antenna multiple output (MIMO)systems have emerged in which mobile terminals incorporate smart antennasystems comprising multiple transmit antenna and multiple receiveantenna. One area of early adoption of MIMO systems has been in thefield of wireless networking, particularly as applied to wireless localarea networks (WLANs) where transmitting mobile terminals communicatewith receiving mobile terminals. IEEE resolution 802.11 comprisesspecifications for communications between mobile terminals in WLANsystems.

Signal fading is a significant problem in wireless communicationssystems, often leading to temporary loss of communications at mobileterminals. One of the most pervasive forms of fading is known asmultipath fading, in which dispersion of transmitted signals due toincident reflections from buildings and other obstacles, results inmultiple versions of the transmitted signals arriving at a receivingmobile terminal. The multiple versions of the transmitted signal mayinterfere with each other and may result in a reduced signal leveldetected at the receiving mobile terminal. When versions of thetransmitted signal are 180° out of phase they may cancel each other suchthat a signal level of 0 is detected. Locations where this occurs maycorrespond to “dead zones” in which communication to the wirelessterminal is temporarily lost. This type of fading is also known as“Rayleigh” or “flat” fading.

A transmitting mobile terminal may transmit data signals in which datais arranged as “symbols”. The transmission of symbols may be constrainedsuch that after a symbol is transmitted, a minimum period of time,T_(s), must transpire before another symbol may be transmitted. Aftertransmission of a symbol from a transmitting mobile terminal, someperiod of dispersion time, T_(d), may transpire which may be the timeover which the receiving mobile terminal is able to receive the symbol,including multipath reflections. The time T_(d) may not need to accountfor the arrival of all multipath reflections because interference fromlater arriving reflected signals may be negligible. If the period T_(s)is less than T_(d) there is a possibility that the receiving mobileterminal will start receiving a second symbol from the transmittingmobile terminal while it is still receiving the first symbol. This mayresult in inter-symbol interference (ISI), producing distortion inreceived signals, and possibility resulting in a loss of information.The quantity 1/T_(d) is also referred to as the “coherence bandwidth”which may indicate the maximum rate at which symbols, andcorrespondingly information, may be transmitted via a givencommunications medium. One method to compensate for ISI in signals mayentail utilizing DSP algorithms which perform adaptive equalization.

Another important type of fading is related to motion. When atransmitting mobile terminal, or a receiving mobile terminal is inmotion, the Doppler phenomenon may affect the frequency of the receivedsignal. The frequency of the received signal may be changed by an amountwhich is a function of the velocity at which a mobile terminal ismoving. Because of the Doppler effect, ISI may result when a mobileterminal is in motion, particularly when the mobile terminal is movingat a high velocity. Intuitively, if a receiving mobile terminal is inmotion and nearing a transmitting mobile terminal, the distance betweenthe two mobile terminals will change as a function of time. As thedistance is reduced, the propagation delay time, T_(p), which is thetime between when a transmitter first transmits a signal and when itfirst arrives at a receiver, is also reduced. As the mobile terminalsbecome closer it is also possible that T_(d) may be increased if, forexample, the transmitting mobile terminal does not reduce the radiatedpower of transmitted signals. If T_(p) becomes less than T_(d), theremay be ISI due to the Doppler effect. This case, which illustrates whydata rates may be reduced for mobile terminals that are in motion, isreferred to as “fast fading”. Because fast fading may distort signals atsome frequencies while not distorting signals at other frequencies, fastfading may also be referred to as “frequency selective” fading.

Smart antenna systems may transmit multiple versions of a signal in whatis known as “spatial diversity”. A key concept in spatial diversity isthat the propagation of multiple versions of a signal, or “spatialstream”, from different antenna may significantly reduce the probabilityof flat fading at the receiving mobile terminal since not all of thetransmitted signals would have the same dead zone.

Current transmission schemes in MIMO systems typically fall into twocategories: data rate maximization, and diversity maximization. Datarate maximization focuses on increasing the aggregate data transfer ratebetween a transmitting mobile terminal and a receiving mobile terminalby transmitting different spatial streams from different antenna. Onemethod for increasing the data rate from a transmitting mobile terminalwould be to decompose a high bit rate data stream into a plurality oflower bit rate data streams such that the aggregate bit rates among theplurality of lower bit rate data streams is equal to that of the highbit rate data stream. Next, each of the lower bit rate data streams maybe mapped to at least one of the transmitting antenna for transmission.In addition, each signal comprising one of the lower bit rate datastreams is multiplicatively scaled by a weighting factor prior totransmission. The plurality of multiplicative scale factors applied tothe plurality of signals comprising the lower bit rate data streams maybe utilized to form the transmitted “beam” in the beamforming technique.An example of a data rate maximization scheme is orthogonal frequencydivision multiplexing (OFDM), in which each of the plurality of signalsis modulated by a different frequency carrier signal prior to mappingand multiplicative scaling. OFDM transmission may be resistant tomultipath fading in that a portion, but most likely not all, of the datatransmitted may be lost at any instant in time due to multipath fading.

Diversity maximization focuses on increasing the probability that asignal transmitted by a transmitting mobile terminal will be received ata receiving mobile terminal, and on increasing the SNR of receivedsignals. In diversity maximization, multiple versions of the same signalmay be transmitted by a plurality of antenna. The case in which atransmitting mobile terminal is transmitting the same signal via all ofits transmitting antenna may be the pure spatial diversity case in whichthe aggregate data transfer rate may be equal to that of a singleantenna mobile terminal. There is a plurality of hybrid adaptations ofthe data rate and spatial diversity maximization schemes which achievevarying data rates and spatial diversities.

MIMO systems employing beamforming may enable the simultaneoustransmission of multiple signals occupying a shared frequency band,similar to what may be achieved in code division multiple access (CDMA)systems. For example, the multiplicative scaling of signals prior totransmission, and a similar multiplicative scaling of signals afterreception, may enable a specific antenna at a receiving mobile terminalto receive a signal which had been transmitted by a specific antenna atthe transmitting mobile terminal to the exclusion of signals which hadbeen transmitted from other antenna. However, MIMO systems may notrequire the frequency spreading techniques used in CDMA transmissionsystems. Thus, MIMO systems may make more efficient utilization offrequency spectrum.

One of the challenges in beamforming is that the multiplicative scalefactors which are applied to transmitted and received signals may bedependent upon the characteristics of the communications medium betweenthe transmitting mobile terminal and the receiving mobile terminal. Acommunications medium, such as a radio frequency (RF) channel between atransmitting mobile terminal and a receiving mobile terminal, may berepresented by a transfer system function, H. The relationship between atime varying transmitted signal, x(t), a time varying received signal,y(t), and the systems function may be represented as shown in equation[1]:y(t)=H×x(t)+n(t), where   equation[1]n(t) represents noise which may be introduced as the signal travelsthrough the communications medium and the receiver itself. In MIMOsystems, the elements in equation[1] may be represented as vectors andmatrices. If a transmitting mobile terminal comprises M transmittingantenna, and a receiving mobile terminal comprises N receiving antenna,then y(t) may be represented by a vector of dimensions N×1, x(t) may berepresented by a vector of dimensions M×1, n(t) by a vector ofdimensions N×1, and H may be represented by a matrix of dimensions N×M.In the case of fast fading, the transfer function, H, may itself becometime varying and may thus also become a function of time, H(t).Therefore, individual coefficients, h_(ij)(t), in the transfer functionH(t) may become time varying in nature.

In MIMO systems which communicate according to specifications in IEEEresolution 802.11, the receiving mobile terminal may compute H(t) eachtime a frame of information is received from a transmitting mobileterminal based upon the contents of a preamble field in each frame. Thecomputations which are performed at the receiving mobile terminal mayconstitute an estimate of the “true” values of H(t) and may be known as“channel estimates”. For a frequency selective channel there may be aset of H(t) coefficients for each tone that is transmitted via the RFchannel. To the extent that H(t), which may be referred to as the“channel estimate matrix”, changes with time and to the extent that thetransmitting mobile terminal fails to adapt to those changes,information loss between the transmitting mobile terminal and thereceiving mobile terminal may result.

Higher layer communications protocols, such as the transmission controlprotocol (TCP) may attempt to adapt to detected information losses, butsuch adaptations may be less than optimal and may result in slowerinformation transfer rates. In the case of fast fading, the problem mayactually reside at lower protocol layers, such as the physical (PHY)layer, and the media access control (MAC) layer. These protocol layersmay be specified under IEEE 802.11 for WLAN systems. The method by whichadaptations may be made at the PHY and MAC layers, however, may comprisea mechanism by which a receiving mobile terminal may provide feedbackinformation to a transmitting mobile terminal based upon channelestimates which are computed at the receiving mobile terminal.

Existing closed loop receiver to transmitter mechanisms, also referredas “RX to TX feedback mechanisms”, that exist under IEEE 802.11 includeacknowledgement (ACK) frames, and transmit power control (TPC) requestsand reports. The TPC mechanisms may allow a receiving mobile terminal tocommunicate information to a transmitting mobile terminal about thetransmit power level that should be used, and the link margin at thereceiving mobile terminal. The link margin may represent the amount ofsignal power that is being received, which is in excess of a minimumpower required by the receiving mobile terminal to decode messageinformation, or frames, that it receives.

A plurality of proposals is emerging for new feedback mechanisms ascandidates for incorporation in IEEE resolution 802.11. Among theproposals for new feedback mechanisms are proposals from TGn (task groupN) sync, which is a multi-industry group that is working to defineproposals for next generation wireless networks which are to besubmitted for inclusion in IEEE 802.11, and Qualcomm. The proposals maybe based upon what may be referred as a “sounding frame”. The soundingframe method may comprise the transmitting of a plurality of longtraining sequences (LTSs) that match the number of transmitting antennaat the receiving mobile terminal. The sounding frame method may notutilize beamforming or cyclic delay diversity (CDD). In the soundingframe method, each antenna may transmit independent information.

The receiving mobile terminal may estimate a complete reverse channelestimate matrix, H_(up), for the channel defined in an uplink directionfrom the receiving mobile terminal to the transmitting mobile terminal.This may require calibration with the transmitting mobile terminal wherethe transmitting mobile terminal determines the forward channel estimatematrix, H_(down), for the channel defined in a downlink direction fromthe transmitting mobile terminal to the receiving mobile terminal. Tocompensate for possible differences between H_(up) and H_(down) thereceiving mobile terminal may be required to receive H_(down) from thetransmitting mobile terminal, and to report H_(up)−H_(down) as feedbackinformation. The TGn sync proposal may not currently define acalibration response. A channel estimate matrix may utilize 24 or morebits for each channel and for each tone, comprising 12 or more bits inan in-phase (I) component and 12 or more bits in a quadrature (Q)component.

According to the principle of channel reciprocity, the characteristicsof the RF channel in the direction from the transmitting mobile terminalto the receiving mobile terminal may be the same as the characteristicsof the RF channel in the direction from the receiving mobile terminal tothe transmitting mobile terminal H_(up)=H_(down). In actual practice,however, there may be differences in the electronic circuitry betweenthe respective transmitting mobile terminal and receiving mobileterminal such that, in some cases, there may not be channel reciprocity.This may require that a calibration process be performed in which H_(up)and H_(down) are compared to reconcile differences between the channelestimate matrices. However, there may be limitations inherent in somecalibration processes. For example, some proposals for new IEEE 802.11feedback mechanisms may be limited to performing “diagonalcalibrations”. These methods may not be able to account for conditionsin which there are differences in non-diagonal coefficients betweenH_(up) and Hd_(down). These non-diagonal coefficient differences may bethe result of complicated antenna couplings at the respectivetransmitting mobile terminal and/or receiving mobile terminal.Accordingly, it may be very difficult for a calibration process tocorrect for these couplings. The ability of a calibration technique toaccurately characterize the RF channel at any instant in time may bedependent upon a plurality of dynamic factors such as, for example,temperature variations. Another limitation of calibration procedures isthat it is not known for how long a calibration renders an accuratecharacterization of the RF channel. Thus, the required frequency atwhich the calibration technique must be performed may not be known.

Further limitations and disadvantages of conventional and traditionalapproaches will become apparent to one of skill in the art, throughcomparison of such systems with some aspects of the present invention asset forth in the remainder of the present application with reference tothe drawings.

BRIEF SUMMARY OF THE INVENTION

Certain embodiments of the invention may be found in a method and systemfor MIMO channel measurement exchange. Aspects of a method forcommunicating information in a communication system may comprisetransmitting data via a plurality of radio frequency (RF) channelsutilizing a plurality of transmitting antenna, receiving feedbackinformation via at least one of the plurality of RF channels, andmodifying a transmission mode based on the feedback information.Feedback information may be requested utilizing at least one of theplurality of transmitting antenna via at least one of the plurality ofRF channels. The number of transmitting antenna utilized during thetransmitting of data may be modified based on the feedback information.The transmission characteristics of data transmitted via at least one ofthe plurality of transmitting antenna may be modified based on thefeedback information. Specific feedback information may be requested inrequest messages.

The method may further comprise negotiating a transmission mode for thetransmitting of data via at least one of the plurality of RF channels.Aspects of the method may further comprise receiving feedbackinformation comprising channel estimates based on the transmissioncharacteristics of the data transmitted by at least one of the pluralityof transmitting antenna. Feedback information may be derived frommathematical matrix decomposition of the channel estimates. Furthermore,feedback information may be derived from mathematical averaging of theresult of mathematical matrix decomposition of the channel estimates.Feedback information may also be derived from a calibration of thechannel estimates for communication in at least one direction via atleast one of the plurality of RF channels.

In another embodiment of the invention a method for communicatinginformation in a communication system may comprise receiving data via aplurality of RF channels utilizing a plurality of receiving antenna,transmitting feedback information via at least one of the plurality ofRF channels, and requesting modification of the transmission mode forreceived data in transmitted response messages comprising the feedbackinformation. Requests for feedback information may be received utilizingat least one of the plurality of receiving antenna via at least one ofthe plurality of RF channels. There may be requests for modification inthe number of transmitting antenna utilized during transmission ofreceived data in the transmitted response messages comprising thefeedback information. There may be requests for modification in thetransmission characteristics of data received via at least one of theplurality of receiving antenna in the transmitted response messagescomprising the feedback information. The response messages may comprisethe feedback information requested in the request messages.

The method may further comprise negotiating the transmission mode forthe data received via at least one of the plurality of RF channels.Aspects of the method may further comprise transmitting feedbackinformation comprising channel estimates based on the transmissioncharacteristics of the data received via at least one of the pluralityof receiving antenna. Feedback information may be derived frommathematical matrix decomposition of the channel estimates. Furthermore,feedback information may be derived from mathematical averaging of theresult of mathematical matrix decomposition of the channel estimates.Feedback information may also be derived from a calibration of thechannel estimates for communication in at least one direction via atleast one of the plurality of RF channels.

Certain aspects of a system for communicating information in acommunication system may comprise a transmitter that transmits data viaa plurality of RF channels utilizing a plurality of transmittingantenna, with the transmitter receiving feedback information via atleast one of the plurality of RF channels, and with the transmittermodifying a transmission mode based on the feedback information. Thetransmitter may request feedback information utilizing at least one ofthe plurality of transmitting antenna via at least one of the pluralityof RF channels. The number of transmitting antenna utilized during thetransmitting of data may be modified based on the feedback information.The transmission characteristics of data transmitted via at least one ofthe plurality of transmitting antenna may be modified based on thefeedback information. The transmitter may request specific feedbackinformation in request messages.

The system may further comprise the transmitter negotiating atransmission mode for the transmitting of data via at least one of theplurality of RF channels. Aspects of the system may further comprisereceiving feedback information comprising channel estimates based on thetransmission characteristics of the data transmitted by at least one ofthe plurality of transmitting antenna. Feedback information may bederived from mathematical matrix decomposition of the channel estimates.Furthermore, feedback information may be derived from mathematicalaveraging of the result of mathematical matrix decomposition of thechannel estimates. Feedback information may also be derived from acalibration of the channel estimates for communication in at least onedirection via at least one of the plurality of RF channels.

These and other advantages, aspects and novel features of the presentinvention, as well as details of an illustrated embodiment thereof, willbe more fully understood from the following description and drawings.

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is an exemplary diagram illustrating wireless communicationbetween two mobile terminals in accordance with an embodiment of theinvention.

FIG. 2 is an exemplary diagram illustrating Eigen beamforming inaccordance with an embodiment of the invention.

FIG. 3 is an exemplary diagram illustrating the MIMO mode request framein accordance with an embodiment of the invention.

FIG. 4 is an exemplary diagram illustrating the MIMO mode response framein accordance with an embodiment of the invention.

FIG. 5 is an exemplary diagram illustrating the MIMO channel requestframe in accordance with an embodiment of the invention.

FIG. 6 a is an exemplary diagram illustrating the MIMO channel responseframe in accordance with an embodiment of the invention.

FIG. 6 b is an exemplary diagram illustrating the MIMO channel responsefield for type=“Complete Channel” in accordance with an embodiment ofthe invention.

FIG. 6 c is an exemplary diagram illustrating the MIMO channel responsefield for type=“SVD Reduced Channel” in accordance with an embodiment ofthe invention.

FIG. 6 d is an exemplary diagram illustrating the MIMO channel responsefield for type=“Null” in accordance with an embodiment of the invention.

FIG. 7 is an exemplary flowchart illustrating steps in the exchange ofRX/TX feedback information utilizing MIMO mode request and MIMO moderesponse frames in accordance with an embodiment of the invention.

FIG. 8 is an exemplary flowchart illustrating steps in the exchange ofRX/TX feedback information utilizing MIMO channel request and MIMOchannel response frames in accordance with an embodiment of theinvention.

DETAILED DESCRIPTION OF THE INVENTION

Certain embodiments of the invention may be found in a method and systemfor MIMO channel measurement exchange. There are options to conventionalmethods of RX/TX feedback mechanisms and to other proposals for newRX/TX feedback mechanisms. In one embodiment of the invention, areceiving mobile terminal may periodically transmit feedbackinformation, comprising a channel estimate matrix, H_(up), to atransmitting mobile terminal. In another embodiment of the invention, areceiving mobile terminal may perform a singular value decomposition(SVD) on the channel estimate matrix, and subsequently transmitSVD-derived feedback information to the transmitting mobile terminal.Utilizing SVD may increase the amount of computation required at thereceiving mobile terminal but may reduce the quantity of informationwhich is transmitted to the transmitting mobile terminal via the RFchannel in comparison to transmitting the entire channel estimatematrix. Yet another embodiment of the invention may expand upon themethod utilizing sounding frames to incorporate calibration. In thisaspect of the invention, a receiving mobile terminal, after transmittinga sounding frame, may subsequently receive a channel estimate matrix,H_(down), from the transmitting mobile terminal. The receiving mobileterminal may then transmit feedback information which is based upon thedifference H_(up)−H_(down), to the transmitting mobile terminal.

One embodiment of the invention may comprise a MIMO channel probe andresponse method, which may provide a flexible solution for RX/TXfeedback because it may support a plurality of feedback mechanisms. Inthis regard, a transmitting mobile terminal may query a receiving mobileterminal to provide feedback information about the transmit modeconfiguration to use. The transmitting mobile terminal may receivefeedback information comprising a full channel estimate matrix ascomputed by a receiving mobile terminal. Alternatively, the transmittingmobile terminal may receive feedback information comprisingdecomposition matrices that were derived from a full channel estimatematrix, or the transmitting mobile terminal may receive feedbackinformation comprising matrices which contain averaged values derivedfrom the decomposition matrices. Furthermore, the transmitting mobileterminal may receive feedback information which may be utilized in acalibration procedure.

RX/TX feedback mechanisms may be required to achieve high informationtransfer rates even in fast fading RF channels. In fast fading RFchannels, however, the channel estimate matrix H(t) may change rapidly.Thus, the amount of feedback information that is required may alsoincrease. Transmission of a large quantity of RT/TX feedback informationmay create excessive overhead on the RF channel and may reduce theavailable rate at which other information transfer may occur via the RFchannel.

SVD is a method which may reduce the quantity of channel feedbackinformation which is transmitted between a receiving mobile terminal anda transmitting mobile terminal. U.S. application Ser. No. ______(Attorney Docket No. 16307US02) describes SVD and is hereby incorporatedby reference herein in its entirety. When computing the SVD a pluralityof techniques may be utilized in performing SVD reduction on the fullchannel estimate matrix. In one embodiment of the invention, a fullchannel estimate matrix which is computed by a receiving mobileterminal, H_(est), may be represented by its SVD:H_(est)=USV^(H), where  equation[2]H_(est) may be a complex matrix of dimensions N_(rx)xN_(tx), whereN_(rx) may be equal to the number of receive antenna at the receivingmobile terminal, and N_(tx) may be equal to the number of transmitantenna at the transmitting mobile terminal, U may be an orthonormalcomplex matrix of dimensions N_(rx)xN_(rx), S may be a diagonal realmatrix of dimensions N_(rx)xN_(tx), and V may be an orthonormal complexmatrix of dimensions N_(tx)xN_(tx) with V^(H) being the Hermitiantransform of the matrix V. The singular values in the matrix S mayrepresent the square roots of the Eigenvalues for the matrix H_(est), Umay represent the left singular vectors for the matrix H_(est) where thecolumns of U may be the Eigenvectors of the matrix productH_(est)H_(est) ^(H), and V^(H) may represent the right singular vectorsfor the matrix H_(est) where the columns of V may be the Eigenvectors ofthe matrix product H_(est) ^(H)H_(est).

If we define a square N_(tx)xN_(tx) matrix, W=H_(est) ^(H)H_(est), thenfor any given Eigenvalue of H_(est), λ, the following relationship mayexist for a nonzero vector, R:WR=λR  equation[3]From which it follows:(H _(est) ^(H) H _(est)-λI)R=0, where  equation[4]I may be the identity matrix.

Solving equation[4], which may also be known as a “characteristicequation”, may produce a set of Eigenvalues. By using each of theseEigenvalues iteratively in equation[4], a series of Eigenvectors, R, maybe derived. The series of Eigenvectors, R, may form the columns of thematrix V.

Since H_(est) ^(H)H_(est)=VS²V^(H), given a matrix of Eigenvectors, V,and a diagonal matrix of Eigenvalues, S, a matrix H_(est) may bederived. Therefore, the channel estimate matrix H_(est) from the SVD inequation[2] may be reconstructed by a transmitting mobile terminal fromfeedback information which contains V^(H) and S only. Since N_(rx) maybe greater than N_(tx), the quantity of information contained inmatrices V^(H) and S may be less than that contained in the matrixH_(est). In an embodiment of the invention, each of the complexcoefficients of the V^(H) matrix may be encoded utilizing, for example,a signed 12-bit integer for an I component, and a signed 12-bit integerfor a Q component. Each of the nonzero diagonal real coefficients of theS matrix may be encoded as, for example, IEEE 32-bit floating pointnumbers.

For an RF channel, H_(est) may be different for tones of differentfrequencies that are transmitted via the RF channel. Thus, a pluralityof channel estimate matrices, H_(est) , may be computed to account foreach tone which may be transmitted via the RF channel. In anotherembodiment of the invention, a further reduction in the quantity ofinformation that is transmitted in feedback information may be achievedby computing a plurality of SVD on H_(est) as in equation[2], andaveraging the coefficient values in matrices V^(H) and S over aplurality of tones. In one aspect of the invention, if M tones aretransmitted via the RF channel, an adaptive modulation technique may beutilized, for example, and a diagonal matrix D derived based upon anaverage of the individual matrices S_(i) that are derived from each ofthe tones: $\begin{matrix}{D = {{1/M} \times {\sum\limits_{i = 1}^{M}S_{i}}}} & {{equation}\lbrack 5\rbrack}\end{matrix}$Adaptive modulation may limit the representation of each nonzerocoefficient in the diagonal matrix, d_(ii) to 8 bits per averaged tone.Thus by replacing the plurality of matrices S_(i) with the matrix D, thequantity of singular value matrix information which is transmitted infeedback information may be reduced by a factor of 4M.

A plurality of L matrices, Avg_(k)(V^(H)), may be derived by averagingthe coefficients from the matrices V^(H) in groups of 6 tones.Furthermore, the matrix of complex coefficient average values may berepresented in the form:Avg _(k)(V(f)^(H))=|Avg_(k)(V(f)^(H))|e ^(jφ), where  equation[6]V(f)^(H) expresses V^(H) as a function of frequency, |Avg_(k)(V(f)^(H))|may represent the magnitude of the average of the I and Q componentsamong the plurality of 6 V(f)^(H) matrices whose coefficients areaveraged in a group, and φ may represent the phase of the correspondingI and Q components, the index k may indicate an individual matrix ofaveraged values of V^(H), and L may equal M/6. In an exemplaryembodiment of the invention, the magnitude |Avg_(k)(V(f)^(H))| may berepresented as a 6-bit integer, and the phase φ may be represented as a4-bit integer. By replacing the plurality of M matrices, V^(H), with aplurality of L matrices Avg(V(f)^(H)), the quantity of singular vectorinformation which is transmitted in feedback information may be reducedby a factor of 6×(24/10).

The invention is not limited to an average of singular values asexpressed in equation[5] and the invention is not limited to expressingthe average as an 8-bit binary data entity. Similarly, the invention asexpressed in equation[6] is not limited to computing averages in groupsof 6 tones, and the invention is not limited to expressing themagnitudes of the averages as 6-bit integers and the phases of theaverages as 4-bit integers. Other possibilities exist and arecontemplated as falling within the scope of the present invention.

In another embodiment of the invention, a calibration procedure may beperformed between the transmitting mobile terminal and the receivingmobile terminal. In this case, the transmitting mobile terminal maycompute a full channel estimate matrix, H_(down). The transmittingmobile terminal may transmit H_(down) to the receiving mobile terminal.The receiving mobile terminal may then perform an SVD on H_(down) toderive matrices, S_(down), and V_(down) ^(H) based on the setting ofU_(down) equal to the value of U that is derived from H_(est) inequation[2]. Furthermore, the receiving mobile terminal may deriveD_(down) and Avg_(k)(V_(down)(f)^(H)). The receiving mobile terminal mayperform calibration by comparing the matrix D_(down) to the matrix D asderived in equation[5]:DΔ=D _(down) −D  equation[7]and by comparing the plurality of matrices Avg_(k)(V_(down)(f)^(H)) tothe plurality of matrices Avg_(k)(V(f)^(H)) as derived in equation[6]:Avg _(k)(VΔ)=Avg _(k)(V _(down)(f)^(H))−Avg _(k)(V(f)^(H))  equation[8]

If Avg_(k)(VΔ) is equal to 0 for all values k=1, . . . L, then the SVDfrom equation[2] may be reconstructed at the transmitting mobileterminal by sending the matrix DΔ only. If Avg_(k)(VΔ) is not equal to 0for all values k=1, . . . L, then the SVD from equation[2] may bereconstructed at the transmitting mobile terminal by sending the matrixDΔ and the plurality of nonzero coefficients from the matricesAvg_(k)(VΔ).

FIG. 1 is an exemplary diagram illustrating wireless communicationbetween two mobile terminals in accordance with an embodiment of theinvention. Referring to FIG. 1 there is shown a first mobile terminal102, a second mobile terminal 122 and a radio frequency (RF)communication channel 150. An example of a standard method by which afirst mobile terminal 102 and a second mobile terminal 122 maycommunicate via an RF channel 150 may be defined in IEEE resolution802.11n. A plurality of different frequencies may be utilized tocommunicate via the RF channel 150 and one or more frequencies may beutilized to communicate information between the first mobile terminal102 and a second mobile terminal 122.

The first mobile terminal 102 may further comprise a coding processor104, a modulation block 106, a mapping block 108, a weighing block 110,and one or more antenna such as the plurality of antenna 112, . . . 114.The second mobile terminal 122 may further comprise one or more antennasuch as the plurality of antenna 124, . . . 126, a weighing block 128, ademapping block 130, a demodulation block 132, and a decoding processor134.

The coding processor 104 may comprise suitable logic, circuitry and/orcode that may be adapted to perform coding on information which is to betransmitted by the transmitting mobile terminal such as, for example,binary convolutional coding (BCC). The modulation block 106 may comprisesuitable logic, circuitry and/or code that may be adapted to modulatebaseband information into one or more RF signals. The mapping block 108may comprise suitable logic, circuitry and/or code that may be adaptedto assign an RF signal for transmission via one or more antenna 112, . .. 114. The weighing block 110 may comprise suitable logic, circuitryand/or code that may be adapted to assign scale factors, or weights, toindividual RF signals for transmission via one or more antenna 112, . .. 114.

In the second mobile terminal 122, one or more antenna 124, . . . 126may receive information from the first mobile terminal 102 via one ormore frequencies over the RF communication channel 150. The weighingblock 128 may comprise suitable logic, circuitry and/or code that may beutilized to assign weights to individual RF signals received via one ormore antenna 124, . . . 126. The demapping block 130 may comprisesuitable logic, circuitry and/or code that may be utilized to reconcilea set of RF signals received from one or more antenna 124, . . . 126into another set of one or more RF signals. The demodulation block 132may comprise suitable logic, circuitry and/or code that may be adaptedto demodulate one or more RF signals into one or more baseband signals.The decoding processor 134 may comprise suitable logic, circuitry and/orcode that may be adapted to perform decoding of information receivedfrom one or more antenna 124, . . . 126 into, for example, binaryinformation.

FIG. 2 is an exemplary diagram illustrating Eigen beamforming inaccordance with an embodiment of the invention. Referring to FIG. 2there is shown a transmitting mobile terminal 202, a receiving mobileterminal 222, and a plurality of RF channels 242. The transmittingmobile terminal 202 comprises a transmit filter coefficient block V 204,a first source signal s₁ 206, a second source signal S₂ 208, a thirdsource signal S₃ 210, and a plurality of transmitting antenna 212, 214,and 216.

In operation, the transmitting antenna 212 may be adapted to transmit asignal x₁, the transmitting antenna 214 may transmit a signal x₂, andthe transmitting antenna 216 may transmit a signal X₃. In beamformingeach transmitted signal x₁, x₂, and X₃ may be a function of a weightedsummation of at least one of the plurality of the source signals s₁, s₂,and s₃. The weights may be determined by the transmit filter coefficientblock V such that:X=VS, where  equation[9]S may be represented by, for example, a 3×1 matrix {s₁, s₂, s₃}, and Xmay be represented by, for example, a 3×1 matrix {x₁, x₂, x₃}.Accordingly, V may be represented as a 3×3 matrix {{v₁₁, v₁₂, v₁₃}{v₂₁,v₂₂, v₂₃}{v₃₁, v₃₂, v₃₃}}.

The receiving mobile terminal 222 comprises a receive filter coefficientblock U* 224, a first destination signal {tilde over (y)}₁ 226, a seconddestination signal {tilde over (y)}₂ 228, a third destination signal{tilde over (y)}₃ 230, and a plurality of receiving antenna 232, 234,and 236. The receiving antenna 232 may be adapted to receive a signaly₁, the receiving antenna 234 may receive a signal Y₂, and the receivingantenna 236 may receive a signal y₃. The characteristics of theplurality of RF channels 242 utilized for communication between thetransmitting mobile terminal 202, and the receiving mobile terminal 222may be represented mathematically by a transfer coefficient matrix H.

FIG. 3 is an exemplary diagram illustrating the MIMO mode request framein accordance with an embodiment of the invention. Referring to FIG. 3there is shown a MIMO mode request frame 300, which comprises a categoryfield 302, an action field 304, a dialog token field 306, and a moderequest field 308. The category field 302 may comprise 1 octet of binarydata, for example, which may identify the general category of the framewithin the wider context of all frames which are defined in IEEE 802.11.The category field 302 may be set to a specific value to identify thecategory which is defined for the MIMO mode request frame. The actionfield 304 may comprise 1 octet of binary data, for example, which mayidentify the frame type. The action field 304 may be set to a specificvalue to identify a MIMO mode request frame. The dialog token field 306may comprise 1 octet of binary data, for example, which may identify aparticular MIMO mode request frame. This field may be utilized toidentify a specific MIMO mode request frame in the event that atransmitting mobile terminal 202 has transmitted a plurality of MIMOmode request frames, such as may be the case if a transmitting mobileterminal 202 were communicating with a plurality of receiving mobileterminals 222.

The mode request field 308 may comprise 1 octet of binary data, forexample, which may identify the function which is to be performed by themobile terminal that receives the MIMO mode request frame. The moderequest field 308 may be set to a specific value to indicate thatfeedback information about the transmit mode to be utilized whentransmitting to a receiving mobile terminal 222 is being requested bythe transmitting mobile terminal 202. The mode request field 308 mayalso comprise information which indicates capabilities of thetransmitting mobile terminal 202. A receiving mobile terminal 222 thatreceives the MIMO mode request frame may use information aboutcapabilities of the transmitting mobile terminal 202 in providingfeedback information to the transmitting mobile terminal 202 in responseto the MIMO mode request frame.

The MIMO mode request frame 300 may be transmitted by a transmittingmobile terminal 202 to a receiving mobile terminal 222 via an RF channel242 to request that the receiving mobile terminal 222 provide feedbackinformation about the transmit mode that the transmitting mobileterminal 202 should use when transmitting information to the receivingmobile terminal 222 via the RF channel 242.

FIG. 4 is an exemplary diagram illustrating the MIMO mode response framein accordance with an embodiment of the invention. Referring to FIG. 4there is shown a MIMO mode response frame 400, which comprises acategory field 402, an action field 404, a dialog token field 406, and amode response field 408. The category field 402 may comprise 1 octet ofbinary data, for example, which may identify the general category of theframe within the wider context of all frames which are defined in IEEE802.11. The category field 402 may be set to a specific value toidentify the category which is defined for the MIMO mode response frame.The action field 404 may comprise 1 octet of binary data, for example,which may identify the frame type. The action field 404 may be set to aspecific value to identify a MIMO mode response frame. The dialog tokenfield 406 may comprise 1 octet of binary data, for example, which mayidentify a particular MIMO mode response frame. This field may beutilized to identify a specific MIMO mode response frame to atransmitting mobile terminal 202.

The mode response field 408 may comprise feedback information, which maybe fed back in response to a previous MIMO mode request frame. The moderesponse field 408 may comprise 4 octets of binary data, for example.The mode response field 408 may comprise feedback information pertainingto a number of spatial streams that a transmitting mobile terminal 202may utilize when transmitting to a receiving mobile terminal 222, anumber of transmit antenna that a transmitting mobile terminal 202 mayutilize, and bandwidth that may be utilized by a transmitting mobileterminal 202. In addition, the mode response field 408 may comprisefeedback information about a code rate to use for informationtransmitted by a transmitting mobile terminal 202, an error correctingcode type to use, and a type of modulation to use for informationtransmitted by a transmitting mobile terminal 202 to a receiving mobileterminal 222. A receiving mobile terminal 222 may indicate a nullresponse in the mode request field 408 to indicate, for example, thatthe receiving mobile terminal 222 is unable to determine a requestedtransmit mode in response to a MIMO mode request frame 300.

The MIMO mode response frame 400 may be transmitted by a receivingmobile terminal 222 to a transmitting mobile terminal 202 in response toa previous MIMO mode request frame 300 to provide feedback informationabout the transmit mode that the transmitting mobile terminal 202 shoulduse when transmitting information to the receiving mobile terminal 222via the RF channel 242.

In an embodiment of the invention with reference to FIGS. 2-4, thetransmitting mobile terminal 202 may transmit a MIMO mode request frame300 to a receiving mobile terminal 222. In the MIMO mode request frame300 an integer value, seq, may be contained in the dialog token field306 of the MIMO mode request frame 300. If the receiving mobile terminal222 incorporates the value, seq, in the dialog token field 406 in theMIMO mode response frame 400, the transmitting mobile terminal 202 whichreceives the MIMO mode response frame 400 may be able to identify theframe as being the response to the MIMO mode request frame 300 that hadbeen sent previously by the transmitting mobile terminal 202 to thereceiving mobile terminal 222.

In another embodiment of the invention, the transmitting mobile terminal202 may transmit a first MIMO mode request frame 300 to a firstreceiving mobile terminal 222. The transmitting mobile terminal 202 maythen transmit a second MIMO mode request frame to a second receivingmobile terminal. In the first MIMO mode request frame an integer value,seq1, may be contained in the dialog token field 306 of the MIMO moderequest frame 300. In the second MIMO mode request frame an integervalue, seq2, may be contained in the dialog token field 306 of the MIMOmode request frame 300. If the first receiving mobile terminal 222incorporates the value, seq1, in the dialog token field 406 in the MIMOmode response frame 400, the transmitting mobile terminal 202 whichreceives the MIMO mode response frame 400 may be able to identify theframe as being the response to the first MIMO mode request frame 300that had been sent previously by the transmitting mobile terminal 202 tothe first receiving mobile terminal 222. If the second receiving mobileterminal 222 incorporates the value, seq2, in the dialog token field 406in the MIMO mode response frame 400, the transmitting mobile terminal202 which receives the MIMO mode response frame 400 may be able toidentify the frame as being the response that corresponds to the secondMIMO mode request frame 300 that had been sent previously by thetransmitting mobile terminal 202 to the second receiving mobileterminal.

Any individual field in either the MIMO mode request frame 300 or theMIMO mode response frame 400 may comprise a plurality of octets ofbinary data. The MIMO mode request frame 300, the MIMO mode responseframe 400, and any individual field in either the MIMO mode requestframe 300 or the MIMO mode response frame 400 may be of variable length.The MIMO mode request frame 300 or the MIMO mode response frame 400 maycomprise information which indicates the length of the respective frame.The MIMO mode request frame 300 or the MIMO mode response frame 400 maycomprise information which indicates the length of any fields containedwithin the respective frame. The MIMO mode request frame 300 and theMIMO mode response frame 400 may comprise other information which enablea receiving mobile terminal 222 and a transmitting mobile terminal 202to negotiate a transmission mode for a common RF channel.

FIG. 5 is an exemplary diagram illustrating the MIMO channel requestframe in accordance with an embodiment of the invention. Referring toFIG. 5 there is shown a MIMO channel request frame 500, which comprisesa category field 502, an action field 504, a dialog token field 506, anda MIMO channel request field 508. The category field 502 may comprise 1octet of binary data, for example, which may identify the generalcategory of the frame within the wider context of all frames which aredefined in IEEE 802.11. The category field 502 may be set to a specificvalue to identify the category which is defined for the MIMO channelrequest frame. The action field 504 may comprise 1 octet of binary data,for example, which may identify the frame type. The action field 504 maybe set to a specific value to identify a MIMO channel request frame. Thedialog token field 506 may comprise 1 octet of binary data, for example,which may identify a particular MIMO channel request frame. This fieldmay be utilized to identify a specific MIMO channel request frame in theevent that a transmitting mobile terminal 202 has transmitted aplurality of MIMO channel request frames, such as may be the case if atransmitting mobile terminal 202 were communicating with a plurality ofreceiving mobile terminals 222.

The MIMO channel request frame 500 may be transmitted by a transmittingmobile terminal 202 to a receiving mobile terminal 222 via an RF channel242 to request that the receiving mobile terminal 222 provide feedbackinformation about the channel estimates that the receiving mobileterminal 222 has computed for the RF channel 242.

The MIMO channel request field 508 may comprise 1 octet of binary data,for example, which may identify the function which is to be performed bythe mobile terminal that receives the MIMO channel request frame. Thechannel request field 508 may be set to a specific value to indicatethat feedback information about the channel estimates that the receivingmobile terminal 222 has computed for the RF channel 242 is beingrequested by the transmitting mobile terminal 202. The MIMO channelrequest field 508 may also comprise information from the channelestimation matrix, H_(down), which is computed at the transmittingmobile terminal 202. A receiving mobile terminal 222 that receives theMIMO channel request frame may use H_(down) information from thetransmitting mobile terminal 202 to perform calibration.

FIG. 6 a is an exemplary diagram illustrating the MIMO channel responseframe in accordance with an embodiment of the invention. Referring toFIG. 6 a there is shown a MIMO channel response frame 600, whichcomprises a category field 602, an action field 604, a dialog tokenfield 606, and a MIMO channel response field 608. The category field 602may comprise 1 octet of binary data, for example, which may identify thegeneral category of the frame within the wider context of all frameswhich are defined in IEEE 802.11. The category field 602 may be set to aspecific value to identify the category which is defined for the MIMOchannel response frame. The action field 604 may comprise 1 octet ofbinary data, for example, which may identify the frame type. The actionfield 604 may be set to a specific value to identify a MIMO channelresponse frame. The dialog token field 606 may comprise 1 octet ofbinary data, for example, which may identify a particular MIMO channelresponse frame. This field may be utilized to identify a specific MIMOchannel response frame to a transmitting mobile terminal 202.

The MIMO channel response field 608 may comprise a variable number ofoctets of binary data, for example, which may comprise feedbackinformation in response to a previous MIMO channel request frame. FIG. 6b is an exemplary diagram illustrating the MIMO channel response fieldfor type=“complete channel” in accordance with an embodiment of theinvention. The length subfield 612 within the MIMO channel responsefield 608 may comprise 2 octets of binary data, for example, which maycomprise information which indicates the length of the MIMO channelresponse field 608. The type subfield 614 within the MIMO channelresponse field may comprise 1 octet of binary data, for example, whichmay comprise information that indicates the feedback information whichis contained the MIMO channel response field 608. In FIG. 6 b thefeedback information type is shown to indicate “complete channel”.Subfield 616 within the MIMO channel response field 608 may comprise 1octet of binary data, for example, which may comprise an indication ofthe number of rows in the matrix of feedback information which iscontained in the MIMO channel response field 608. Subfield 618 withinthe MIMO channel response field 608 may comprise 1 octet of binary data,for example, which may comprise an indication of the number of columnsin the matrix of feedback information which is contained in the MIMOchannel response field 608. Subfield 620 within the MIMO channelresponse field 608 may comprise a variable number of octets based uponthe contents of subfields 616 and 618, for example, which may comprisethe complete channel estimate matrix which was computed duringprocessing of the preceding MIMO channel request frame 500.

FIG. 6 c is an exemplary diagram illustrating the MIMO channel responsefield for type=“SVD Reduced Channel” in accordance with an embodiment ofthe invention. The length subfield 632 within the MIMO channel responsefield 608 may comprise 2 octets of binary data, for example, which maycomprise information which indicates the length of the MIMO channelresponse field 608. The type subfield 634 within the MIMO channelresponse field may comprise 1 octet of binary data, for example, whichmay comprise information that indicates the feedback information whichis contained the MIMO channel response field 608. In FIG. 6 c thefeedback information type is shown to indicate “SVD reduced channel”.Subfield 636 within the MIMO channel response field 608 may comprise 1octet of binary data, for example, which may comprise an indication ofthe number of rows in the matrix of feedback information which iscontained in the MIMO channel response field 608. Subfield 638 withinthe MIMO channel response field 608 may comprise 1 octet of binary data,for example, which may comprise an indication of the number of columnsin the matrix of feedback information which is contained in the MIMOchannel response field 608. Subfield 640 within the MIMO channelresponse field 608 may comprise a variable number of octets based uponthe contents of subfields 636 and 638, for example, which may comprisethe right singular vector matrix, V. Subfield 642 within the MIMOchannel response field 608 may comprise a variable number of octetsbased upon the contents of subfields 636 and 638, for example, which maycomprise the diagonal matrix of singular values, S. The matrices V and Smay be derived from the complete channel estimate matrix which wascomputed during the processing of the preceding MIMO channel requestframe 500.

FIG. 6 d is an exemplary diagram illustrating the MIMO channel responsefield for type=“Null” in accordance with an embodiment of the invention.The length subfield 652 within the MIMO channel response field 608 maycomprise 2 octets of binary data, for example, which may compriseinformation which indicates the length of the MIMO channel responsefield 608. The type subfield 654 within the MIMO channel response fieldmay comprise 1 octet of binary data, for example, which may compriseinformation that indicates the feedback information which is containedthe MIMO channel response field 608. In FIG. 6 d the feedbackinformation type is shown to indicate “Null”. If the feedbackinformation type is “null”, the receiving mobile terminal 222 may nothave been able to compute a channel estimate, in which case the MIMOchannel response field 608 may not comprise feedback information.

The MIMO channel response frame 600 may be transmitted by a receivingmobile terminal 222 to a transmitting mobile terminal 202 in response toa previous MIMO channel request frame 500 to provide feedbackinformation about the channel estimates that the receiving mobileterminal 222 has computed for the RF channel 242.

If the quantity of data from SVD derived matrices are further reduced byaveraging, the MIMO channel response field 608 may comprise anindication of the number of rows in the matrices which are contained inthe MIMO channel response field 608, an indication of the number ofcolumns in the matrices which are contained in the MIMO channel responsefield, the matrix D as derived in equation[5], and the plurality ofmatrices Avg_(k)(V(f)^(H)) as derived in equation[6]. If the calibrationprocedure is used, the MIMO channel response field 608 may comprise anindication of the number of rows in the matrices which are contained inthe MIMO channel response field 608, an indication of the number ofcolumns in the matrices which are contained in the MIMO channel responsefield 608, the matrix DΔ as derived in equation[7], and the matrixAvg_(k)(VΔ) as derived in equation[8].

The initial MIMO channel request frame 500 may be sent by thetransmitting mobile terminal 202 to the receiving mobile terminal 222without beamforming, and utilizing a number of spatial streams may equalthe number of antenna. For each spatial stream, the lowest data rate maybe used when transmitting the MIMO channel request frame 500 to enablethe transfer of information between the transmitting mobile terminal 202and receiving mobile terminal 222 to be as robust as possible. Forexample, with reference to FIG. 2, without beamforming antenna 212 maytransmit a signal which is proportional to signal s₁ 206 only, whileantenna 214 may transmit a signal which is proportional to signal s₂ 208only, and antenna 216 may transmit a signal which is proportional tosignal s₃ 210 only such that:X=cS, where  equation[10]S may be represented by a 3×1 matrix {s₁, s₂, s₃}, X may be representedby a 3×1 matrix {x₁, x₂, x₃}, and c may be a scalar entity.

Any individual field in either the MIMO channel request frame 500 or theMIMO channel response frame 600 may comprise a plurality of octets ofbinary data. The MIMO channel request frame 500, the MIMO channelresponse frame 600, and any individual field in either the MIMO channelrequest frame 500 or the MIMO channel response frame 600 may be ofvariable length. The MIMO channel request frame 500 or the MIMO channelresponse frame 600 may comprise information which indicates the lengthof the respective frame. The MIMO channel request frame 500 or the MIMOchannel response frame 600 may comprise information which indicates thelength of any fields contained within the respective frame. The MIMOchannel request frame 500 and the MIMO channel response frame 600 maycomprise other information which enable a receiving mobile terminal 222to communicate feedback information about the channel estimates that thereceiving mobile terminal 222 has computed for the RF channel 242 to atransmitting mobile terminal 202.

FIG. 7 is an exemplary flowchart illustrating steps in the exchange ofRX/TX feedback information utilizing MIMO mode request and MIMO moderesponse frames in accordance with an embodiment of the invention.Referring to FIG. 7, in step 702 a transmitting mobile terminal 202 maysend a MIMO mode request frame to a receiving mobile terminal 222. Instep 704 the receiving mobile terminal 222 may receive the MIMO moderequest frame from the transmitting mobile terminal 202. In step 706 thereceiving mobile terminal 222 may determine the transmitting mode. Ifthe receiving mobile terminal 222 determines the transmitting mode, instep 710, the receiving mobile terminal 222 may transmit a MIMO moderesponse frame to the transmitting mobile terminal 202 containinginformation about the desired transmitting mode. If the receiving mobileterminal 222 does not determine the transmitting mode, in step 708, thereceiving mobile terminal 222 may transmit a MIMO mode response frame tothe transmitting mobile terminal 202 which contains no feedbackinformation on the desired transmitting mode.

FIG. 8 is an exemplary flowchart illustrating steps in the exchange ofRX/TX feedback information utilizing MIMO channel request and MIMOchannel response frames in accordance with an embodiment of theinvention. Referring to FIG. 8, in step 802 a transmitting mobileterminal 202 may send a MIMO channel request frame to a receiving mobileterminal 222. In step 804 the receiving mobile terminal 222 may receivethe MIMO channel request frame from the transmitting mobile terminal202. In step 806 the receiving mobile terminal 222 may determine whethera null response is to be returned to the transmitting mobile terminal202. If a null response is to be returned, in step 808, the receivingmobile terminal 222 may transmit a MIMO channel response frame to thetransmitting mobile terminal 202 containing null channel information.

If a null response is not to be sent, in step 810 the receiving mobileterminal may determine whether to send a complete channel response. If acomplete channel response is to be sent, in step 812 the receivingmobile terminal 222 may transmit a MIMO channel response frame to thetransmitting mobile terminal 202 containing the number of transmitantenna, the number of receive antenna, and a complete channel estimatematrix computed during the processing of the preamble field in thepreceding MIMO channel request frame.

If a complete channel response is not to be sent, in step 814, thereceiving mobile terminal 222 may compute a complete channel estimatematrix based on the preamble field in the preceding MIMO channel requestframe. In step 816, the receiving mobile terminal 222 may compute thematrix decomposition on the complete channel estimate matrix. In step816, matrix decomposition on the complete channel estimate matrix may beperformed by a plurality of methods comprising SVD, QR decomposition,lower diagonal, diagonal, upper diagonal (LDU) decomposition, andCholesky decomposition. In step 818, the receiving mobile terminal 222may transmit a MIMO channel response frame to the transmitting mobileterminal 202 containing the number of transmit antenna, the number ofreceive antenna, the right singular vector matrix, and the diagonalmatrix of singular values.

The channel feedback method may enable more precise estimation of RFchannel characteristics than is possible with conventional IEEE 802.11systems, or when utilizing other proposals for new RX/TX feedbackmechanisms. In conventional IEEE 802.11 specifications, there may be nofeedback mechanism by which the receiving mobile terminal 222 mayindicate a specific transmitting mode to be utilized by a transmittingmobile terminal 202. Consequently, in conventional systems based uponIEEE 802.11, the transmitting mobile terminal 202 may independentlyselect a transmitting mode with no mechanism by which the transmittingmode may be adapted to the requirements of the receiving mobile terminal222. The MIMO mode response mechanism may enable a receiving mobileterminal 222 to suggest a particular transmitting mode to thetransmitting mobile terminal 202.

The channel feedback method described may enable the receiving mobileterminal 222 to efficiently communicate feedback information, to thetransmitting mobile terminal 202, about the characteristics of the RFchannel 242 as detected at the receiving mobile terminal 222. Inresponse, the transmitting mobile terminal 202 may adapt the RF signalsthat are transmitted to the receiving mobile terminal 222 based upon thechannel feedback information received from the receiving mobile terminal222. Embodiments of the invention which have been described may minimizethe quantity of feedback information and thereby reduce the amount ofoverhead imposed on the RF channel as a result of RX/TX feedback. Thismay enable the channel feedback mechanism to be utilized effectively infast fading RF channels. As a result, the channel feedback method mayenable the transmitting mobile terminal to achieve higher informationtransfer rates, and more effective beamforming on signals that aretransmitted to the receiving mobile terminal via an RF channel.

The invention may not be limited to the SVD method to reduce the amountof feedback information which is sent via an RF channel. A plurality ofmethods may be utilized for reducing the quantity of feedbackinformation when compared to the amount of information that is containedin a full channel estimate matrix. These methods may comprise, forexample, SVD, LDU decomposition, Eigenvalue decomposition, QRdecomposition, and Cholesky decomposition.

Accordingly, the present invention may be realized in hardware,software, or a combination of hardware and software. The presentinvention may be realized in a centralized fashion in at least onecomputer system, or in a distributed fashion where different elementsare spread across several interconnected computer systems. Any kind ofcomputer system or other apparatus adapted for carrying out the methodsdescribed herein is suited. A typical combination of hardware andsoftware may be a general-purpose computer system with a computerprogram that, when being loaded and executed, controls the computersystem such that it carries out the methods described herein.

The present invention may also be embedded in a computer programproduct, which comprises all the features enabling the implementation ofthe methods described herein, and which when loaded in a computer systemis able to carry out these methods. Computer program in the presentcontext means any expression, in any language, code or notation, of aset of instructions intended to cause a system having an informationprocessing capability to perform a particular function either directlyor after either or both of the following: a) conversion to anotherlanguage, code or notation; b) reproduction in a different materialform.

While the present invention has been described with reference to certainembodiments, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted withoutdeparting from the scope of the present invention. In addition, manymodifications may be made to adapt a particular situation or material tothe teachings of the present invention without departing from its scope.Therefore, it is intended that the present invention not be limited tothe particular embodiment disclosed, but that the present invention willinclude all embodiments falling within the scope of the appended claims.

1. A method for communicating information in a communication system, themethod comprising: transmitting data via a plurality of radio frequency(RF) channels utilizing a plurality of transmitting antenna; receivingfeedback information via at least one of said plurality of RF channels,and; modifying a transmission mode based on said feedback information.2. The method according to claim 1, further comprising requesting saidfeedback information utilizing at least one of said plurality oftransmitting antenna via said at least one of said plurality of RFchannels.
 3. The method according to claim 1, further comprisingmodifying a number of said plurality of transmitting antenna utilizedduring said transmitting data based on said feedback information.
 4. Themethod according to claim 1, further comprising modifying transmissioncharacteristics of said transmitted data via at least one of saidplurality of transmitting antenna based on said feedback information. 5.The method according to claim 1, further comprising requesting specificsaid feedback information in request messages.
 6. The method accordingto claim 1, further comprising negotiating said transmission mode forsaid transmitted data via said at least one of said plurality of RFchannels.
 7. The method according to claim 1, further comprisingreceiving said feedback information comprising channel estimates basedon transmission characteristics of said transmitted data via at leastone of said plurality of transmitting antenna.
 8. The method accordingto claim 7, further comprising deriving said feedback information frommathematical matrix decomposition of said channel estimates.
 9. Themethod according to claim 7, further comprising deriving said feedbackinformation from mathematical averaging of a result of mathematicalmatrix decomposition of said channel estimates.
 10. The method accordingto claim 7, further comprising deriving said feedback information fromcalibration of said channel estimates for communication in at least onedirection via said at least one of said plurality of RF channels.
 11. Amethod for communicating information in a communication system, themethod comprising: receiving data via a plurality of RF channelsutilizing a plurality of receiving antenna; transmitting feedbackinformation via at least one of said plurality of RF channels, and;requesting modification of a transmission mode for said received data intransmitted response messages comprising said feedback information. 12.The method according to claim 11, further comprising receiving requestsfor said feedback information utilizing at least one of said pluralityof receiving antenna via said at least one of said plurality of RFchannels.
 13. The method according to claim 11, further comprisingrequesting modification in a number of transmitting antenna utilizedduring transmission of said received data in said transmitted responsemessages comprising said feedback information.
 14. The method accordingto claim 11, further comprising requesting modification in transmissioncharacteristics of said received data via at least one of said pluralityof receiving antenna in said transmitted response messages comprisingsaid feedback information.
 15. The method according to claim 11, whereinsaid response messages comprise said feedback information requested inrequest messages.
 16. The method according to claim 11, furthercomprising negotiating said transmission mode for said received data viasaid at least one of said plurality of RF channels.
 17. The methodaccording to claim 11, further comprising transmitting said feedbackinformation comprising channel estimates based on transmissioncharacteristics of said received data via at least one of said pluralityof receiving antenna.
 18. The method according to claim 17, furthercomprising deriving said feedback information from mathematical matrixdecomposition of said channel estimates.
 19. The method according toclaim 17, further comprising deriving said feedback information frommathematical averaging of a result of mathematical matrix decompositionof said channel estimates.
 20. The method according to claim 17, furthercomprising deriving said feedback information from calibration of saidchannel estimates for communication in at least one direction via saidat least one of said plurality of RF channels.
 21. A system forcommunicating information in a communication system, the systemcomprising: a transmitter that transmits data via a plurality of RFchannels utilizing a plurality of transmitting antenna; said transmitterreceives feedback information via at least one of said plurality of RFchannels, and; said transmitter modifies a transmission mode based onsaid feedback information.
 22. The system according to claim 21, whereinsaid transmitter requests said feedback information utilizing at leastone of said plurality of transmitting antenna via said at least one ofsaid plurality of RF channels.
 23. The system according to claim 21,wherein said transmitter modifies a number of said plurality oftransmitting antenna utilized during said transmitting data based onsaid feedback information.
 24. The system according to claim 21, whereinsaid transmitter modifies transmission characteristics of saidtransmitted data via at least one of said plurality of transmittingantenna based on said feedback information.
 25. The system according toclaim 21, wherein said transmitter requests specific said feedbackinformation in request messages.
 26. The system according to claim 21,wherein said transmitter negotiates said transmission mode for saidtransmitted data via said at least one of said plurality of RF channels.27. The system according to claim 21, wherein said transmitter receivessaid feedback information comprising channel estimates based ontransmission characteristics of said transmitted data via at least oneof said plurality of transmitting antenna.
 28. The system according toclaim 27, wherein said transmitter derives said feedback informationfrom mathematical matrix decomposition of said channel estimates. 29.The system according to claim 27, wherein said transmitter derives saidfeedback information from mathematical averaging of a result ofmathematical matrix decomposition of said channel estimates.
 30. Thesystem according to claim 27, wherein said transmitter derives saidfeedback information from calibration of said channel estimates forcommunication in at least one direction via said at least one of saidplurality of RF channels.